1. Field of the Invention
This invention relates to a system for passing solid objects by a pipeline pumping station.
2. Prior Art
In the long distance pipeline transportation of liquids and gases, it is a common practice to insert solid objects into the pipeline. The solid objects may be the primary products being transprted in the pipeline, in which case they are generally called "capsules". Capsules may consist entirely of a solid product, or may consist of a solid, gel or liquid product that is encapsulated in a solid or flexible membrane. The solid objects may also be used to separate batches of fluid, in which case they are generally called "spacers" or "displacers". Or, the solid objects may be equipped with brushes or scrapers to clean the internal pipeline wall, in which case they are generally called "scrapers". Such objects are usually spherical or cylindrical in shape, having an external diameter slightly less than the internal diameter of the pipeline and are usually made of a hard or resilient material. All of these objects may fall under the classification of pipeline capsules or pigs.
Pipelines that cover long distances generally have booster pumping stations to maintain desired flow rates. When pipeline capsules, pigs or other solid objects are present in the flowing fluid, it is either necessary to provide a way to remove them from the fluid upstream from the pumping station and then reinject them at a point downstream from the station, or to provide a way for passing the solid objects by the station without removing them from the main pipeline. The latter may be accomplished by shutting the pump station down and opening a valve located in the main pipeline between the station suction and discharge lines to allow the flowing fluid to carry the solid object past the pump station. This method can be economically unattractive, particularly when there are several solid objects in the fluid stream, since pressure surges are created when the pumping system is shut-down and then subsequently restarted. This method also results in the mixing of fluids immediately preceding the solid object in the pipeline with fluids immediately following the solid object, as the fluids preceding the solid object are retained in the pump station piping when the station is shut down.
Several systems defined in the patent literature teach passing solid objects by a pumping station:
U.S. Pat. No. 3,212,116 to Gentry, Jr. teaches a pipeline scraper passing system which senses the arrival of a scraper upstream from a pumping station and switches the inlet and outlet for the station to a point upstream from the scraper. After passage of the scraper, the system is returned to normal operation.
U.S. Pat. No. 3,664,356 to Grove et al. teaches a system for removing separator spheres from a pipeline and then reinjecting them into the line at a point downstream from a pumping station. Timing devices are employed to provide for injection of the spheres at the interface region between different products in the pipeline.
U.S. Pat. No. 3,678,950 to Ragsdale teaches a system for passing a batch of slurry around a pumping station by sensing the slurry approaching the upstream side of the station inlet and switching the station inlet and outlet to a point upstream from the slurry batch.
U.S. Pat. No. 3,682,186 to Howe teaches a system for passing a scraper by a pump station which uses a pig sensing device and timing controller to redirect pump inlet and discharge flow. Pumping is returned through the normal flow channels after the scraper has passed the station.
None of the prior art pump station bypassing systems provide for the continuous unidirectional flow of the primary fluid while passing a solid object past the pump station.